TCP/IP attachment considerations

To print at rated speed on high speed printers, not only must the printer be able to process and image the data at high speeds, but the system and communications link must also be able to provide data to the printer fast enough to maintain this speed. PSF provides significant improvement in the ability to deliver data over a TCP/IP link to high-speed production printers. This improvement lets PSF support TCP/IP-attached InfoPrint 3000, InfoPrint 4000, and InfoPrint 4100 printer families, and the InfoPrint 5000.

The ability to run production printing applications at rated speed on printers that are attached directly to PSF over TCP/IP depends on these factors:

• Number of printers and the printing speeds
• Density of the application data stream, typically measured in average bytes per page
• Availability of processor resources
• LAN bandwidth and use

Density of the application data stream can be a critical factor. TCP/IP-attached printers are able to receive about 1 megabyte of data per second. Although this amount is adequate for printing text jobs at rated speed on most high-speed printers or jobs with some image content on printers with lower rated speeds, some image intensive jobs might contain too much data to print at rated speed on some printers when TCP/IP-attached.

You can estimate the data rate that is required to run an application at rated speed on a specific printer with this calculation:

     bytes per second = (average bytes per page) x (pages per minute) 
                        --------------------------------------------- 
                                              60 

Average bytes per page includes bytes of data on the page and AFP control bytes, which vary with the complexity of the application formatting. In addition, AFP resources that are loaded on the printer can add to the average byte load of a print job.

With PSF, FICON® channel-attachment provides the fastest and most performance efficient attachment for high-speed production printers. As with using TCP/IP for other applications, using PSF with TCP/IP-attached printers requires more processor resource than using ESCON® or parallel channel, for the same printers and applications. In general, TCP/IP attachment uses about the same amount of processor as SNA-communication attachment.

For best performance, each TCP/IP-attached printer should be on a dedicated segment of a token-ring or Ethernet LAN, with the TCP/IP maximum transmission unit (MTU) size that is set to the largest supported value. Attachment through token ring might provide better performance for some applications than attachment through Ethernet, especially if the LAN is not dedicated.